KR102161626B1 - Negative electrode and lithium battery including the same - Google Patents

Abstract

Disclosed are a negative electrode, a lithium battery employing the same, and a method of manufacturing the same. The negative electrode includes a current collector and a negative active material layer disposed on at least one surface of the current collector, and the negative active material layer includes metal nanoparticles, a carbon-based material, titanium-containing oxide, and a binder. The titanium-containing oxide is included in the negative electrode active material layer having a density of more than 1.5 g/cc and less than 3 g/cc, thereby improving high rate characteristics of a battery.

Description

Negative electrode and lithium battery including the same

It relates to a negative electrode and a lithium battery employing the same.

Lithium secondary batteries are charged with an organic electrolyte or polymer electrolyte between a positive electrode and a negative electrode including an active material capable of intercalating and deintercalating lithium ions, and are subjected to oxidation and reduction reactions when lithium ions are inserted/desorbed from the positive electrode and the negative electrode. Produces electrical energy.

Carbon-based materials are widely used as negative active materials for lithium secondary batteries, and examples thereof include crystalline carbon such as graphite and artificial graphite, and amorphous carbon such as soft carbon and hard carbon. However, even if such a carbon-based material has a high theoretical capacity, it is only about 380 mAh/g, and there is a problem that it is difficult to use in a high-capacity lithium battery.

In order to improve such problems, a metal capable of forming an alloy by reacting with lithium such as silicon, tin, aluminum, germanium, lead, etc., and related alloys and composites are being actively studied. It is believed that a negative electrode active material using such a non-elastic material can occlude and release more lithium ions than a negative electrode active material including a carbon-based material, so that a battery having a high capacity and high energy density can be manufactured. For example, pure silicon is known to have a high theoretical capacity of 4,200 mAh/g.

In addition, as the field of small-sized high-tech devices such as digital cameras, mobile devices, notebook computers, and computers has been developed, miniaturization of lithium secondary batteries, which are energy sources, has been achieved. In order to reduce the size of the battery, it is required to use a battery having a high energy density. Even if the material has a large capacity, when the density of the negative active material layer is low, the energy density cannot be increased.

Accordingly, there is a need for a negative electrode capable of implementing a high capacity and increasing the density of the negative active material layer.

An aspect of the present invention includes a current collector and a negative active material layer disposed on at least one surface of the current collector, the negative active material layer comprises metal nanoparticles, a carbon-based material, and a titanium-containing oxide, and the negative active material layer It is to provide a negative electrode having a density of greater than 1.5 g/cc and less than 3 g/cc.

Another aspect of the present invention is to provide a lithium battery with improved lifespan characteristics employing the negative electrode.

In one aspect of the present invention,

Current collector; And an anode active material layer disposed on at least one surface of the current collector, wherein the anode active material layer includes metal nanoparticles, a carbon-based material, titanium-containing oxide and a binder, and the density of the anode active material layer is 1.5 g/ A negative electrode for a lithium battery having more than cc and less than 3 g/cc is provided.

According to an embodiment, the titanium-containing oxide may include lithium titanate represented by Formula 1:

<Formula 1>

Li _x Ti _y M _z O _n

In the above formula, 1≦x≦4, 1≦y≦5, 0≦z≦3 and 3≦n≦12, and M is Li, Mg, Al, Ca, Sr, Cr, V, Fe, Co, Ni, Zr, Zn, Si, P, S, Y, Nb, Ga, Sn, Mo, W, Ba, La, Ce, Ag, Ta, Hf, Ru, Bi, Sb and at least one selected from the group consisting of As It is an element.

According to an embodiment, the titanium-containing oxide is Li ₂ TiO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₃ O ₇ , LiCrTiO ₄ , LiFeTiO ₄ , Li ₂ TiSiO ₅ , LiTiPO ₅ and LiTi ₂ (PO ₄ ) It may contain at least one lithium titanate selected from the group consisting of ₃ .

According to an embodiment, the titanium-containing oxide may include a compound represented by Formula 2:

<Formula 2>

Ti _y M _z O _n

In the above formula, 1≦y≦2, 0≦z≦2 and 1≦n≦7, and M is Li, Mg, Al, Ca, Sr, Cr, V, Fe, Co, Ni, Zr, Zn, Si, It is at least one element selected from the group consisting of P, S, Y, Nb, Ga, Sn, Mo, W, Ba, La, Ce, Ag, Ta, Hf, Ru, Bi, Sb and As.

According to an embodiment, the titanium-containing oxide may include at least one compound selected from the group consisting of TiO ₂ , TiSO ₅ , TiP ₂ O ₇ and TiP ₂ O ₇ .

According to an embodiment, the titanium-containing oxide may include a compound represented by Formula 3:

<Formula 3>

Li _{x +3} Ti _y O ₁₂

In the above formula, 2.4≦x≦4.2 and 4.8<y≦6.6.

According to an embodiment, the titanium-containing oxide may be an inert material that does not occlude or release lithium ions during charging and discharging of a lithium battery.

According to an embodiment, the titanium-containing oxide may have electrical conductivity.

According to an embodiment, the content of the titanium-containing oxide may be 1% to 20% by weight based on the total weight of the negative active material layer.

According to an embodiment, the metal nanoparticles may include at least one selected from the group consisting of Si, Sn, Al, Ge, Pb, Bi, Sb, alloys thereof, and oxides thereof.

According to an embodiment, the metal nanoparticles may include Si or SiO _x (0<x<2).

According to an embodiment, the metal nanoparticles may include metal nanoparticles having a carbon-based coating layer formed thereon.

According to an embodiment, the content of the metal nanoparticles may be 0.1% to 50% by weight based on the total weight of the negative active material layer.

According to an embodiment, the carbon-based material may include crystalline carbon, amorphous carbon, or a mixture thereof.

According to an embodiment, the content of the carbon-based material may be 50% to 90% by weight based on the total weight of the negative active material layer.

According to an embodiment, the negative active material layer may further include a binder.

According to an embodiment, the binder is polyvinylidene fluoride, polyvinylidene chloride, polybenzimidazole, polyimide, polyvinyl acetate, polyacrylonitrile, polyvinyl alcohol, carboxymethylcellulose (CMC), Starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyaniline, acrylonitrile butadiene styrene, phenolic resin, epoxy Resin, polyethylene terephthalate, polytetrafluoroethylene, polyphenyl sulfide, polyamideimide, polyetherimide, polyethylene sulfone, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, or a combination thereof.

According to an embodiment, the negative active material layer may further include a conductive material.

In another aspect of the present invention, a lithium battery including the negative electrode is provided.

The negative electrode according to an embodiment includes a current collector and a negative active material layer disposed on at least one surface of the current collector, and the negative active material layer includes metal nanoparticles, a carbon-based material, and a titanium-containing oxide. The titanium-containing oxide is included in the negative electrode active material layer having a density of more than 1.5 g/cc and less than 3 g/cc, thereby improving high rate characteristics of a battery.

Accordingly, it is possible to implement a battery having a high density negative active material layer and exhibiting high output.

1 is a schematic diagram showing the structure of a lithium battery structure according to an embodiment.
2 is a graph showing the capacity retention rate according to the C-rate of lithium batteries manufactured according to Comparative Example 5 and Comparative Example 6.
3 is a graph showing the capacity retention rate according to the C-rate of lithium batteries prepared according to Example 3 and Comparative Example 7.
4 is a graph showing a capacity retention rate for each cycle of a lithium battery manufactured according to Example 3.

Hereinafter, the present invention will be described in more detail.

In general, when manufacturing a negative electrode, after coating a negative electrode active material composition on a current collector, a rolling process is performed to densify the electrode and reduce resistance. In this case, in order to reduce the thickness of the negative active material layer formed after the rolling process and to achieve high capacity under a given volume condition of a battery, the density of the negative active material layer must be high.

That is, "the density of the active material layer (g/cc)" refers to the mass per volume of the active material layer, and is also called a mix density, and is a measure of the degree to which the electrode plate is pressed during the rolling process.

However, in the case of using a negative active material such as silicon in order to realize a high capacity of the battery, increasing the density of the negative active material layer by a certain level or more reduces the voids in the negative active material layer, thereby reducing the overall physical properties of the battery such as high rate characteristics. There was a problem.

Accordingly, the present inventors have implemented a battery with improved high rate characteristics and output characteristics, even when increasing the density of the negative electrode active material layer by using an oxide containing titanic acid.

Specifically, the negative electrode for a lithium battery according to one aspect, the current collector; And an anode active material layer disposed on at least one surface of the current collector, wherein the anode active material layer includes metal nanoparticles, a carbon-based material, and titanium-containing oxide, and the density of the anode active material layer is greater than 1.5 g/cc It is less than 3 g/cc.

In the case of a battery employing a negative electrode having a density of the negative active material layer of 1.5 g/cc or less, high rate characteristics may not be deteriorated even if the titanium-containing oxide is not included.

However, in the case of a battery employing a negative electrode having a density of the negative electrode active material layer greater than 1.5 g/cc, the pores between the metal nanoparticles and the carbon-based material are reduced, so that impregnation of the electrolyte may be difficult. This is because the metal nanoparticles have a very large volume change during charging and discharging of the battery, and thus it is difficult to contribute to increasing the density of the negative electrode active material layer.

On the other hand, unlike the metal nanoparticles, the titanium-containing oxide has a small volume change during charging and discharging and has a high tap density, thus contributing to increasing the density of the negative active material layer. Therefore, by using an appropriate amount of the titanium-containing oxide, in the negative electrode active material layer having a density of more than 1.5 g/cc and less than 3 g/cc, an appropriate level of pore structure can be secured. As a result, wettability for the electrolyte solution is improved, and high rate characteristics and output characteristics of the battery may be improved.

Moreover, since the titanium-containing oxide has a high average voltage at which lithium ions are intercalated/desorbed, it is not involved in the formation of a film capable of increasing resistance, so that a high capacity can be maintained even at a high rate.

According to an embodiment, the titanium-containing oxide may include lithium titanate represented by the following Formula 1:

<Formula 1>

Li _x Ti _y M _z O _n

In the above formula, 1≦x≦4, 1≦y≦5, 0≦z≦3 and 3≦n≦12, and M is Li, Mg, Al, Ca, Sr, Cr, V, Fe, Co, Ni, Zr, Zn, Si, P, S, Y, Nb, Ga, Sn, Mo, W, Ba, La, Ce, Ag, Ta, Hf, Ru, Bi, Sb and at least one selected from the group consisting of As It is an element.

For example, the titanium-containing oxide is Li ₂ TiO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₃ O ₇ , LiCrTiO ₄ , LiFeTiO ₄ , Li ₂ TiSiO ₅ , LiTiPO ₅ and LiTi ₂ (PO ₄ ) ₃ It may contain at least one lithium titanate selected from the group consisting of.

For example, the titanium-containing oxide may include Li ₄ Ti ₅ O ₁₂ .

According to an embodiment, the titanium-containing oxide may include a compound represented by Formula 2 below:

<Formula 2>

Ti _y M _z O _n

In the above formula, 1≦y≦2, 0≦z≦2 and 1≦n≦7, and M is Li, Mg, Al, Ca, Sr, Cr, V, Fe, Co, Ni, Zr, Zn, Si, It is at least one element selected from the group consisting of P, S, Y, Nb, Ga, Sn, Mo, W, Ba, La, Ce, Ag, Ta, Hf, Ru, Bi, Sb and As.

For example, the titanium-containing oxide may include at least one compound selected from the group consisting of TiO ₂ , TiSO ₅ , and TiP ₂ O ₇ .

According to an embodiment, the titanium-containing oxide may include a compound represented by Formula 3:

<Formula 3>

Li _{x +3} Ti _y O ₁₂

In the above formula, 2.4≦x≦4.2 and 4.8<y≦6.6.

The compound represented by Formula 3 may be an inert material that does not occlude or release lithium ions during charging and discharging of a lithium battery. For example, the compound represented by Formula 3 is a form in which lithium ions are inserted into the titanium-containing oxide when the battery is initially charged, and lithium ions are no longer inserted or desorbed even after repeated charging and discharging. The structure represented by Formula 3 can be maintained.

For example, when the battery including the negative electrode is discharged, the lithium ions inserted during charging are desorbed in metal nanoparticles and carbon-based materials, whereas in the titanium-containing oxide, the discharge end voltage so that the inserted lithium ions are not desorbed during charging. (discharge cut-off voltage) can be set. Accordingly, the structure represented by Chemical Formula 3 in which lithium ions are inserted may be maintained even during repeated charging and discharging.

The compound represented by Formula 3 may have a form in which lithium ions are inserted into lithium titanate represented by the following chemical formula 4:

<Formula 4>

Li _x Ti _y O ₁₂

In the above formula, 2.4≦x≦4.2 and 4.8<y≦6.6.

For example, the titanium-containing oxide may include a Li ₄ Ti ₅ O ₁₂ The lithium ions are inserted into the form of Li ₇ Ti ₅ O ₁₂ in.

In addition, the titanium-containing oxide may have electrical conductivity. Specifically, the titanium-containing oxide may serve as a conductive material, thereby lowering the resistance of the battery including the negative electrode. Accordingly, the negative active material layer may not include a separate conductive material other than the titanium-containing oxide.

The content of the titanium-containing oxide may be 1% to 20% by weight based on the total weight of the negative active material layer. For example, the content of the titanium-containing oxide may be 1% to 15% by weight based on the total weight of the negative active material layer. For example, the content of the titanium-containing oxide may be 5% to 15% by weight based on the total weight of the negative active material layer. In the above range, due to the weight and volume of the titanium-containing oxide that may exist as an inert material, the lithium storage capacity of the negative electrode may not be reduced, and the high rate characteristics may be improved even at a high density of the negative electrode active material layer.

The metal nanoparticles may include at least one selected from the group consisting of Si, Sn, Al, Ge, Pb, Bi, Sb, alloys thereof, and oxides thereof.

For example, the metal nanoparticles may be Si.

For example, the metal nanoparticles are Si-Y alloys (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination element thereof, not Si), Sn- Y alloy (the Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth element, or a combination element thereof, but not Sn), and the like. The element Y is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, It may be Se, Te, Po, or a combination thereof.

For example, the metal nanoparticles may be oxides such as SnO ₂ and SiO _x (0<x<2).

The metal nanoparticles may include metal nanoparticles having a carbon-based coating layer formed thereon.

For example, the metal nanoparticles may be coated with a carbon-based material. The carbon-based material may include amorphous carbon. In this case, the amorphous carbon may be selected from soft carbon, hard carbon, mesophase pitch carbide, fired coke, nano carbon fiber, or a mixture thereof.

The coating method of the carbon-based coating layer is not limited thereto, but both a dry coating method or a liquid coating method may be used. For example, as the dry coating method, chemical vapor deposition (CVD), evaporation, or the like may be used, and as the liquid coating method, impregnation or spraying may be used. When using the liquid coating method, DMSO, THF, etc. can be used as a solvent.

The content of the metal nanoparticles may be 0.1% to 50% by weight based on the total weight of the negative active material layer 20. For example, the content of the metal nanoparticles may be 1% to 30% by weight based on the total weight of the negative active material layer 20. In the above range, while securing the structural stability of the negative electrode, a high-capacity battery can be implemented.

The carbon-based material may include crystalline carbon, amorphous carbon, or a mixture thereof.

The crystalline carbon may be amorphous, plate-like, flake, spherical or fibrous natural graphite, or artificial graphite produced by carbonizing coal-based pitch or petroleum-based pitch. The amorphous carbon may be soft carbon or hard carbon, mesophase pitch carbide, fired coke, etc., but is not limited thereto.

The content of the carbon-based material may be 50% to 90% by weight based on the total weight of the negative active material layer. In the above range, while securing structural stability of the negative electrode, a density of the negative active material layer of a certain level or higher may be realized.

The negative active material layer may further include a binder.

The binder may be an aqueous binder.

For example, the binder is polyvinylidene fluoride (PVdF), polyvinylidene chloride, polybenzimidazole, polyimide, polyvinyl acetate, polyacrylonitrile, polyvinyl alcohol, carboxymethylcellulose (CMC) , Starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyaniline, acrylonitrile butadiene styrene, phenol resin, Epoxy resin, polyethylene terephthalate, polytetrafluoroethylene, polyphenyl sulfide, polyamideimide, polyetherimide, polyethylenesulfone, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, ethylene-propylene-diene Monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, or a combination thereof may be selected, but is not limited thereto. The content of the binder is 1 to 50 parts by weight, for example 1 to 30 parts by weight, for example, based on 100 parts by weight of the sum of metal nanoparticles, carbon-based materials, and titanium-containing oxides that can serve as negative active materials. It may be 1 to 20 parts by weight, or, for example, 1 to 15 parts by weight.

The binder may assist in bonding between the metal nanoparticles and the current collector, bonding the titanium-containing oxide and the current collector, and bonding the metal nanoparticles and the conductive material.

The negative active material layer may further include a conductive material. The conductive material may further improve electrical conductivity by providing a conductive path to the metal nanoparticles, the carbon-based material, and the titanium-containing oxide. As the conductive material, anything generally used for lithium batteries may be used, and examples thereof include carbon-based materials such as carbon black, acetylene black, Ketjen black, and carbon fiber; Metal-based materials such as metal powder or metal fibers such as copper, nickel, aluminum, and silver; A conductive material containing a conductive polymer such as a polyphenylene derivative, or a mixture thereof can be used. The content of the conductive material can be appropriately adjusted and used. For example, the weight ratio of the sum of the metal nanoparticles, the carbon-based material, and the titanium-containing oxide to the conductive material may range from 99:1 to 90:10.

The current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, it may be made of at least one material selected from aluminum, copper, nickel, titanium, and stainless steel. Surface treatment of the material such as aluminum, copper, nickel, stainless steel, etc. by electroplating or ion deposition with coating components such as nickel, copper, aluminum, titanium, gold, silver, platinum, palladium, etc. Nanoparticles may be coated on the surface of the main material through a method such as dip or compression, and may be used as a substrate. In addition, the current collector may be configured in a form in which the above conductive material is coated on a base made of a non-conductive material.

The current collector may have a fine uneven structure formed on its surface, and such an uneven structure can increase adhesion to the active material layer to be coated on the substrate. The current collector may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric. The current collector may generally have a thickness of 3 μm to 500 μm.

A lithium battery according to another aspect of the present invention includes the negative electrode described above.

Hereinafter, a method of manufacturing the aforementioned lithium battery will be described.

The method of manufacturing the lithium battery includes: providing a lithium battery structure including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte; And performing a chemical conversion process on the lithium battery structure to prepare a lithium battery, wherein the providing of the lithium battery structure includes a negative electrode active material composition comprising metal nanoparticles, a carbon-based material, and a titanium-containing oxide Manufacturing a; Applying the negative active material composition on a current collector to prepare a current collector to which the negative active material composition is applied; And drying and rolling the current collector coated with the negative active material composition to prepare a negative electrode having a negative active material layer having a density of greater than 1.5 g/cc and less than 3 g/cc on the current collector.

First, the steps of providing a lithium battery structure including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte are as follows.

The negative electrode may be manufactured as follows.

The anode active material composition may be prepared by dispersing the metal nanoparticles, titanium-containing oxide, carbon-based material, and optionally a binder and a conductive material in a solvent.

Thereafter, the negative active material composition may be coated on a current collector to prepare a current collector in which the negative active material composition is applied on at least one surface, and the coating may be performed by directly coating the negative active material composition on the current collector, or After casting the negative active material composition on a support, a negative active material film peeled from the support may be laminated on a current collector.

Then, the current collector to which the negative active material composition is applied is dried at 80°C to 120°C, and then rolled to prepare a negative electrode having a negative active material layer having a density of more than 1.5 g/cc and less than 3 g/cc.

According to an embodiment, the metal nanoparticles, titanium-containing oxide, carbon-based material, binder, and conductive material included in the negative active material composition are as described above.

According to an embodiment, the titanium-containing oxide included in the negative active material composition may include lithium titanate represented by Formula 4:

<Formula 4>

Li _x Ti _y O ₁₂

In the above formula, 2.4≦x≦4.2 and 4.8<y≦6.6.

The lithium titanate represented by Formula 4 may be in a form before lithium ions are inserted into the compound represented by Formula 3.

For example, lithium titanate represented by Formula 4 may include Li ₄ Ti ₅ O ₁₂ .

In this case, N-methylpyrrolidone (NMP), acetone, water, etc. may be used as the solvent. The content of the solvent may be 1 to 400 parts by weight based on 100 parts by weight of the positive electrode active material. When the content of the solvent is within the above range, the operation for forming the active material layer is easy.

Next, the positive electrode may be manufactured in the same manner as the negative electrode, except that a positive electrode active material is used instead of the metal nanoparticles, titanium-containing oxide, and carbon-based material of the negative electrode. In addition, in the positive electrode active material composition, the binder, the conductive material and the solvent may be the same as those of the negative electrode.

For example, a positive electrode active material composition may be prepared by dispersing a positive electrode active material, a binder, and optionally a conductive material in a solvent. Thereafter, the positive active material composition is directly coated on a current collector, or the positive active material composition is cast on a separate support, and then a positive active material film peeled off from the support is laminated on the current collector, A current collector to which the composition is applied can be prepared. Thereafter, the current collector to which the positive active material composition is applied may be dried and rolled to manufacture a positive electrode having a positive active material layer formed thereon.

As the positive electrode active material, any material commonly used as a positive electrode active material in the art may be used. Specifically, the following compounds may be used independently as cores of the first positive electrode active material and the second positive electrode active material. For _{example, Li a A 1 - b B} b D 2 ( in the above formula, 0.90 ≤ a ≤ 1, and 0 ≤ b ≤ 0.5); Li _a E _{1 -b} B _b O _2-c D _c (where 0.90≦a≦1, 0≦b≦0.5, 0≦c≦0.05); LiE _{2 -b} B _b O _4-c D _c (wherein 0≦b≦0.5, 0≦c≦0.05); Li _a Ni _{1 -b- c} Co _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-α F _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b- c} Co _b B _c O _{2 -α} F ₂ (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _{1 -b- c} Mn _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α ≤ 2); Li _a Ni _{1 -b- c} Mn _b B _c O _{2 -α} F _α (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ (in the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 <α <2); Li _a Ni _b E _c G _d O ₂ (in the above formula, 0.90≦a≦1, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li _a Ni _b Co _c Mn _d GeO ₂ (wherein, 0.90≦a≦1, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); Li _a NiG _b O ₂ (in the above formula, 0.90≦a≦1, 0.001≦b≦0.1); Li _a CoG _b O ₂ (in the above formula, 0.90≦a≦1, 0.001≦b≦0.1); Li _a MnG _b O ₂ (in the above formula, 0.90≦a≦1, 0.001≦b≦0.1); Li _a Mn ₂ G _b O ₄ (In the above formula, 0.90≦a≦1, 0.001≦b≦0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0≦f≦2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≦f≦2); A compound represented by any one of the formulas of LiFePO ₄ can be used:

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or combinations thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

For example, LiCoO ₂ , LiMn _x O _2x (x=1, 2), LiNi _{1 -x} Mn _x O _2x (0<x<1), LiNi _{1 -x- y} Co _x Mn _y O ₂ (0≤ x≤0.5, 0≤y≤0.5), FePO ₄ and the like.

Next, a separator to be inserted between the positive and negative electrodes is prepared. Any of the separators may be used as long as they are commonly used in lithium batteries. Particularly, those having low resistance to ion migration of the electrolyte and excellent electrolyte-moistening ability are suitable. For example, as a material selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene, and combinations thereof, it may be a non-woven fabric or a woven form. The separator is generally used with a pore diameter of 0.01 µm to 10 µm and a thickness of 5 µm to 300 µm.

The electrolyte may be formed of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolyte solution, an organic solid electrolyte, an inorganic solid electrolyte, or the like may be used.

As the non-aqueous electrolyte, for example, N-methyl-2-pyrrolidinone, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl Methyl carbonate (EMC), gamma-butyllolactone (GBL), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyl tetrahydrofuran, dimethyl sulfoxide (DMSO), 1,3 -Dioxolane (DOL), formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate tryster, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1, Aprotic organic solvents such as 3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyropionate, and ethyl propionate may be used.

As the organic solid electrolyte, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a poly agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, Alternatively, a polymer including an ionic dissociating group may be used.

As the inorganic solid electrolyte, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ A nitride, halide, or sulfate of Li such as Li may be used.

Any of the lithium salts can be used as long as they are commonly used in lithium batteries, and as a material that is soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , _{LiPF 6, LiCF 3 SO 3,} LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2) 2 NLi, lithium chloro borate, lower aliphatic carboxylic One or more materials such as lithium main acid, lithium 4 phenyl borate, or imide may be used.

In addition, the electrolyte may include vinylene carbonate (VC), catechol carbonate (CC), and the like to form and maintain the SEI layer on the surface of the negative electrode. Optionally, the electrolyte may include a redox-shuttle additive such as n-butylferrocene and halogen-substituted benzene to prevent overcharging. Optionally, the electrolyte may contain an additive for forming a film such as cyclohexylbenzene or biphenyl. Optionally, the electrolyte may include a cation receptor such as a crown ether compound and an anion receptor such as a boron compound in order to improve conduction properties. Optionally, in the electrolyte, a phosphate-based compound such as trimethyl phosphate (TMP), tris (2,2,2-trifluoroethyl) phosphate (TFP), and hexamethoxycyclotriphosphazene (HMTP) may be added as flame retardant. I can.

If necessary, the electrolyte helps to form a stable SEI layer or film on the electrode surface, so that the safety of the lithium battery can be further improved, for example, tris (trimethylsilyl) phosphate (TMSPa), lithium difluorooxalatoborate. (LiFOB), propanesultone (PS), succitonitrile (SN), LiBF ₄ such as acrylic, amino, epoxy, methoxy, ethoxy, silane compound having a functional group capable of forming a siloxane bond such as vinyl, hexa Silazane compounds such as methyl disilazane, etc., specifically, for example, may further include additives such as propane sultone (PS), succitonitrile (SN), and LiBF ₄ .

For example, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , and LiN(SO ₂ CF ₃ ) ₂ are used as a cyclic carbonate of EC or PC as a highly dielectric solvent and a linear carbonate of DEC, DMC or EMC as a low viscosity solvent. The electrolyte can be prepared by adding it to the mixed solvent of.

1 schematically shows a typical structure of a lithium battery structure according to an embodiment of the present invention.

Referring to FIG. 1, the lithium battery structure 100 includes a positive electrode 93, a negative electrode 92, and a separator 94 disposed between the positive electrode 93 and the negative electrode 92 to form a primary structure. Can be formed. In addition, a separator 94 may be additionally disposed on the outer surface of the anode 93 or the cathode 92 to prevent internal short circuit. Thereafter, the primary structure may be wound or folded, and may be placed in a cylindrical or rectangular battery container 95. Then, after injecting an electrolyte into the battery container 95, the lithium battery structure 100 may be manufactured by sealing with the sealing member 96.

Next, a step of manufacturing a lithium battery by performing a chemical conversion process on the lithium battery structure.

The chemical conversion process is a process of stabilizing a battery structure and making the lithium battery structure usable. For example, the conversion process may include an aging process, a charging process, and a discharging process of the lithium battery structure.

The aging process is a process of impregnating an electrolyte solution into the lithium battery structure.

The charging process is a process of completely charging a battery in order to form a solid electrolyte interphase layer (SEI) on the surface of the negative electrode. In the charging process, lithium ions may be inserted into the metal nanoparticles and the lithium titanate particles.

For example, during the charging process, the lithium titanate particles may have lithium ions inserted into the compound represented by Chemical Formula 2. For example, the lithium titanate particles may be transformed into a compound represented by the following Formula 3 in which lithium ions are inserted into the compound represented by Formula 4:

<Formula 3>

Li _{x +3} Ti _y O ₁₂

In the above formula, 2.4≦x≦4.2 and 4.8<y≦6.6.

The discharging process is a process of completely discharging the battery charged in the charging process, and then a recharging process may be performed for product shipment.

During the discharging process, the cut-off of the lithium battery structure may be performed at a voltage of 0.2 V to 1.5 V.

During the discharging process, at a voltage of 1.5 V or less, the lithium titanate represented by Formula 4 may maintain the form of a compound in which lithium ions are inserted.

Thus, at a voltage of 1.5 V or less during the discharging process, the titanium-containing oxide may include a compound represented by the following formula (3):

<Formula 3>

Li _{x +3} Ti _y O ₁₂

In the above formula, 2.4≦x≦4.2 and 4.8<y≦6.6.

For example, when a cut-off is performed at a voltage of 1.5 V or less during discharge, metal nanoparticles, carbon-based materials, etc. included in the negative electrode of the lithium battery structure may release lithium ions. On the other hand, the titanium-containing oxide may not emit lithium ions. That is, at a voltage of 1.5 V or less during the discharging process, the titanium-containing oxide is not discharged and the charged form of Formula 3 may be maintained.

Therefore, after the chemical conversion process, the titanium-containing oxide is turned into an inert material that no longer occludes or releases lithium ions, thereby effectively performing the role of a conductive material.

A method of using a lithium battery according to another aspect of the present invention includes discharging the above-described lithium battery at a voltage of 1.5 V or less.

By not discharging the lithium battery at a voltage exceeding 1.5 V, it is possible to prevent lithium ions in the titanium-containing oxide from being desorbed.

The lithium battery may be used not only as a battery used as a power source for a small device, but also as a unit cell of a medium or large device battery module including a plurality of batteries.

Examples of the medium and large devices include a power tool; XEVs, including electric vehicles (EV), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); Electric motorcycles including E-bikes and E-scooters; Electric golf cart; Electric truck; Electric commercial vehicles; Or a system for power storage; And the like, but are not limited thereto. In addition, the lithium battery can be used in all other applications requiring high output, high voltage and high temperature driving.

Exemplary embodiments are described in more detail through the following examples and comparative examples. However, the embodiments are for illustrative purposes only, and the scope of the present invention is not limited thereto.

(Manufacture of cathode)

Example One

Si particles with an average particle diameter of 15 nm (manufactured by Sigma Aldrich), Li ₄ Ti ₅ O _{12 with an} average particle diameter of 150 nm (manufactured by Samsung Fine Chemicals), graphite with an average particle diameter of 16 µm (manufactured by Mitsubishi), and a binder Polyacrylonitrile (PAN) was mixed in a weight ratio of 6.65: 9.5: 78.85: 5, and a solvent N-methylpyrrolidone was added so that the solid content was 60% by weight to adjust the viscosity, and the negative active material composition Was prepared.

The negative active material composition was coated on a copper current collector having a thickness of 15 μm using a conventional method to a thickness of about 40 μm. The current collector coated with the composition was dried at room temperature, dried again at 120° C., and rolled to prepare a negative electrode having a negative active material layer having a density of 1.7 g/cc.

Example 2

A negative electrode was prepared in the same manner as in Example 1, except that TiSO ₅ (manufactured by Sigma Aldrich) having an average particle diameter of 150 nm was used.

Comparative example One

A negative electrode was manufactured in the same manner as in Example 1, except that a negative electrode having a negative active material layer having a density of 1.5 g/cc was prepared.

Comparative example 2

Si particles having an average particle diameter of 15 nm (manufactured by Sigma Aldrich), graphite having an average particle diameter of 16 µm (manufactured by Mitsubishi Corporation), and polyacrylonitrile (PAN) as a binder were mixed in a weight ratio of 7.4:9.2:5, In order to adjust the viscosity, a solvent N-methylpyrrolidone was added so that the solid content was 60% by weight, to prepare a negative active material composition.

The negative active material composition was coated on a copper current collector having a thickness of 15 μm using a conventional method to a thickness of about 40 μm. The current collector coated with the composition was dried at room temperature, dried again at 120° C., and rolled to prepare a negative electrode having a negative active material layer having a density of 1.5 g/cc.

Comparative example 3

A negative electrode was manufactured in the same manner as in Comparative Example 2, except that a negative electrode having a negative active material layer having a density of 1.7 g/cc was prepared.

Comparative example 4

A negative electrode was manufactured in the same manner as in Example 2, except that a negative electrode having a negative active material layer having a density of 1.5 g/cc was prepared.

(Manufacture of lithium secondary battery-coin half cell ( coin half cell ))

Example 3

A 2032 standard lithium battery structure was prepared by using the negative electrode prepared in Example 1, lithium metal as a counter electrode, and a polypropylene separator having a thickness of 14 μm, and injecting an electrolyte to compress it. At this time, the electrolyte is a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) (EC:DEC:FEC is 5:70:25 in a volume ratio) of LiPF ₆ is 1.10M What dissolved so as to become a concentration was used.

The lithium battery structure was initially charged at a current of 0.1 C for 10 minutes, and then left at 25° C. for 1 day.

Thereafter, it was charged with a constant current until the voltage reached 4.2V at a current of 0.1C rate. Subsequently, discharge was performed at a constant current of 0.1 C rate until the discharge end voltage reached 1.5 V. (Mars phase)

Subsequently, constant current charging was performed at a current of 0.2C rate until the voltage reached 4.3V, and constant voltage charging was performed until the current reached 0.05C while maintaining 4.3V. Subsequently, discharge was performed at a constant current of 0.2C until the discharge end voltage of 1.5V was reached, thereby preparing a lithium secondary battery. (Rating stage)

Example 4

A lithium secondary battery was manufactured in the same manner as in Example 3, except that the negative electrode prepared in Example 2 was used.

Comparative example 5 to 8

A lithium secondary battery was manufactured in the same manner as in Example 3, except that the negative electrodes prepared in Comparative Examples 1 to 4 were used respectively.

( Evaluation example 1: high rate characteristics evaluation)

The batteries prepared in Example 3-4 and Comparative Example 5-8 were charged with a 0.9V CC (constant current)/CV (constant voltage) 0.01C cutoff and then charged and discharged at a rate of 0.2C After carrying out the cycle of 1.5V cutoff discharge once, the charge/discharge rates were changed to 0.5C, 1.0C, 2.0C, 3.0C and 5.0C, respectively, and the capacity retention rate for each C-rate was measured. Some of the results are shown in FIGS. 2 and 3.

As shown in FIG. 2, in the case of a battery having a density of a negative active material layer of 1.5 g/cc, high rate characteristics are not improved even if Li ₄ Ti ₅ O ₁₂ is included in the negative electrode.

On the other hand, as shown in FIG. 3, when the density of the negative active material layer is increased to 1.7 g/cc, the battery according to Comparative Example 7 in which Li ₄ Ti ₅ O ₁₂ is not included in the negative electrode has capacity at a rate higher than 1.0 C. It was impossible to measure the retention rate. However, the battery according to Example 3 in which Li ₄ Ti ₅ O ₁₂ was included in the negative electrode showed a capacity retention rate of 90% or more even at _5.0 C. Therefore, it can be seen that when Li ₄ Ti ₅ O ₁₂ is included in the negative electrode, high rate characteristics can be improved even if the density of the negative active material layer is increased. This means that the capacity of the battery per hour that can be implemented is increased, and thus it indicates that the output characteristics can also be improved.

( Evaluation example 2: High rate life characteristics evaluation)

The lithium batteries prepared in Example 3-4 and Comparative Example 5-8 were charged at a constant current until the voltage reached 4.3 V at a current of 1.0 C rate at 25° C. and maintained at 4.3 V. While doing, constant voltage charging was performed until the current reached 0.01C. Subsequently, the cycle of discharging with a constant current of 3.0 C was repeated up to 50 times until the voltage reached 1.5 V during discharge.

The capacity retention rate (CRR) of the coin half cell was measured and shown in Table 1 and FIG. 4 below. Here, the capacity retention rate is defined by Equation 1 below.

<Equation 1>

Capacity retention rate [%] = [Discharge capacity in each cycle/1 ^st cycle] × 100

In the cathode
Titanium-containing oxide
Contains or not Of the negative active material layer
density
(g/cc) In episode 50
Capacity retention rate
(%) Example 3 Li ₄ Ti ₅ O ₁₂ 1.7 82 Example 4 TiSO ₅ 1.7 80 Comparative Example 5 Li ₄ Ti ₅ O ₁₂ 1.5 78 Comparative Example 6 - 1.5 82 Comparative Example 7 - 1.7 Not measurable Comparative Example 8 TiSO ₅ 1.5 78

As shown in Table 1, the batteries manufactured according to Comparative Example 5 and Comparative Example 8 did not improve the capacity retention rate at a high rate compared to the batteries manufactured according to Comparative Example 6.

On the other hand, as shown in Tables 1 and 4, the batteries manufactured according to Examples 3 and 4 exhibited improved capacity retention at a high rate compared to the batteries manufactured according to Comparative Example 7. This is Li ₄ Ti ₅ O ₁₂ , TiSO ₅ on the cathode This is because when a lithium-containing oxide such as such is included, even if the density of the negative electrode active material layer is increased, the impregnation property of the electrolyte solution, etc. are not lowered, and high rate life characteristics can be improved.

Accordingly, a battery capable of exhibiting high output while having a high-density negative electrode active material layer may be implemented by using the negative electrode including the lithium-containing oxide.

In the above, preferred embodiments according to the present invention have been described with reference to the drawings and embodiments, but these are only exemplary, and various modifications and other equivalent embodiments are possible from those of ordinary skill in the art. You will be able to understand. Therefore, the scope of protection of the present invention should be determined by the appended claims.

92: cathode 93: anode
94: separator 95: battery container
96: sealing member 100: lithium battery structure

Claims (19)

Current collector; And a negative active material layer disposed on at least one surface of the current collector,
The negative electrode active material layer includes a mixture of metal nanoparticles, a carbon-based material, and a titanium-containing oxide,
The content of the titanium-containing oxide is 1% to 20% by weight based on the total weight of the negative active material layer,
A negative electrode for a lithium battery having a density of the negative active material layer greater than 1.5 g/cc and less than 3 g/cc. The method of claim 1,
A negative electrode for a lithium battery containing lithium titanate, wherein the titanium-containing oxide is represented by the following Formula 1:
<Formula 1>
Li _x Ti _y M _z O _n
In the above formula, 1≦x≦4, 1≦y≦5, 0≦z≦3 and 3≦n≦12, and M is Li, Mg, Al, Ca, Sr, Cr, V, Fe, Co, Ni, Zr, Zn, Si, P, S, Y, Nb, Ga, Sn, Mo, W, Ba, La, Ce, Ag, Ta, Hf, Ru, Bi, Sb and at least one selected from the group consisting of As It is an element. The method of claim 2,
The titanium-containing oxide is selected from the group consisting of Li ₂ TiO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₃ O ₇ , LiCrTiO ₄ , LiFeTiO ₄ , Li ₂ TiSiO ₅ , LiTiPO ₅ and LiTi ₂ (PO ₄ ) ₃ A negative electrode for a lithium battery containing at least one lithium titanate. The method of claim 1,
A negative electrode for a lithium battery including the titanium-containing oxide compound represented by the following formula (2):
<Formula 2>
Ti _y M _z O _n
In the above formula, 1≦y≦2, 0≦z≦2 and 1≦n≦7, and M is Li, Mg, Al, Ca, Sr, Cr, V, Fe, Co, Ni, Zr, Zn, Si, It is at least one element selected from the group consisting of P, S, Y, Nb, Ga, Sn, Mo, W, Ba, La, Ce, Ag, Ta, Hf, Ru, Bi, Sb and As. The method of claim 4,
The titanium-containing oxide is TiO ₂ , TiSO ₅ , TiP ₂ O ₇ and TiP ₂ O _{7 A} negative electrode for a lithium battery comprising at least one compound selected from the group consisting of. The method of claim 1,
A negative electrode for a lithium battery including the titanium-containing oxide compound represented by the following formula (3):
<Formula 3>
Li _{x +3} Ti _y O ₁₂
In the above formula, 2.4≦x≦4.2 and 4.8<y≦6.6. The method of claim 6,
The negative electrode for a lithium battery, wherein the titanium-containing oxide is an inert material that does not occlude or release lithium ions during the charging and discharging process of the lithium battery. The method of claim 6,
A negative electrode for a lithium battery in which the titanium-containing oxide has electrical conductivity. delete The method of claim 1,
The anode for a lithium battery, wherein the metal nanoparticles include at least one selected from the group consisting of Si, Sn, Al, Ge, Pb, Bi, Sb, alloys thereof, and oxides thereof. The method of claim 1,
The negative electrode for lithium batteries wherein the metal nanoparticles include Si or SiO _x (0<x<2). The method of claim 1,
A negative electrode for a lithium battery, wherein the metal nanoparticles include metal nanoparticles having a carbon-based coating layer. The method of claim 1,
A negative electrode for a lithium battery in which the content of the metal nanoparticles is 0.1% to 50% by weight based on the total weight of the negative active material layer. The method of claim 1,
The negative electrode for a lithium battery wherein the carbon-based material contains crystalline carbon, amorphous carbon, or a mixture thereof. The method of claim 1,
A negative electrode for a lithium battery in which the content of the carbon-based material is 50% to 90% by weight based on the total weight of the negative active material layer. The method of claim 1,
A negative electrode for a lithium battery wherein the negative active material layer further includes a binder. The method of claim 16,
The binder is polyvinylidene fluoride, polyvinylidene chloride, polybenzimidazole, polyimide, polyvinyl acetate, polyacrylonitrile, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose Loose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polystyrene, polymethyl methacrylate, polyaniline, acrylonitrile butadiene styrene, phenol resin, epoxy resin, polyethylene terephthalate, Polytetrafluoroethylene, polyphenyl sulfide, polyamideimide, polyetherimide, polyethylene sulfone, polyamide, polyacetal, polyphenylene oxide, polybutylene terephthalate, ethylene-propylene-diene monomer (EPDM), sulfonated A negative electrode for lithium batteries selected from EPDM, styrene butadiene rubber (SBR), fluorine rubber, or a combination thereof. The method of claim 1,
A negative electrode for a lithium battery wherein the negative active material layer further includes a conductive material. A lithium battery comprising the negative electrode according to any one of claims 1 to 8 and 10 to 18.

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